What could have been a simple throw-away character instead evolved into a sidekick in the cartoon series based on the film, The Real Ghostbusters. An early episode of the series shows how Slimer came to be a trusted member of the GB team. Picking up where the movie left off we see the Ghostbusters return from their encounter with Gozer. Still covered in marshmallow, the guys dump their trashed uniforms into the hamper. The uniforms are contaminated with paranormal energy, however, and soon come to life and cause trouble. Slimer shows up at the Ghostbusters' firehouse and, after helping to catch the uniform ghosts, he's allowed to stay and join the team. Throughout the course of the series he's seen helping out and causing mischief.

Slimer's popularity grew quickly and eventually he was even more popular than the Ghostbusters themselves. He began to appear on merchandise, action figures, and drink boxes (such as Hi-C's Ecto Cooler). When the cartoon became Slimer! and The Real Ghostbusters in the late 80s Slimer took the lead of the show in slap-dashly animated segments featuring him roaming the neighborhood with his friends (who, prior to these segments, did not exist) and fighting the neighborhood cat. The animated Slimer also appeared in the 1988 cartoon anti-drug propaganda segment Cartoon All-Stars to the Rescue.

Slimer's popularity led to a cameo in 1989's Ghostbusters II where he's seen briefly in the firehouse eating Louis Tully's lunch. Later in the film he's seen driving the bus that takes Louis to the museum. A deleted scene from the film (but present in the novelization) shows Louis using a spare proton pack to try and catch Slimer, but instead he blasts a hole in the ceiling of the firehouse.

Slimer faded away into 1980s nostalgia along with the rest of the Ghostbusters, but perhaps someday he will return. And when he does chances are he'll be hungry.